Asymmetric Synthesis of 3-Lactone-Substituted 2-Oxindoles with Vicinal Quaternary Carbon Centers through Vinylogous Conjugate Addition

A new method has been developed for constructing vicinal quaternary stereocenters with an oxindole-butanolide hybrid framework through asymmetric vinylogous addition of a siloxyfuran to an indol-2-one in the presence of a readily available N,N'-dioxide-Ni(OTf)(2) complex catalyst. Various oxindole-lactones were obtained in up to 98% yield with >19:1 dr and 97% ee under mild reaction conditions. A possible transition-state model is proposed to explain the origin of the asymmetric induction.